Implantable drug delivery devices are used to deliver various types of therapeutic agents. For example, drug-eluting stents release an anti-proliferative agent such as sirolimus or paclitaxel into the wall of the blood vessel in contact with the stent to prevent fibrosis by implantable polymer reservoirs slowly eluting drug at a pre-determined rate into the surrounding tissue. Previously, it has been difficult to determine whether the therapeutic agent is being or has been correctly released because there may be no way to directly or indirectly visualize changes in the drug delivery device or the mechanism of drug release while the drug delivery device is inside the subject. Release can be confirmed analytically by assaying a blood or tissue sample taken from a patient for the presence of the therapeutic agent or by looking for the expected clinical improvement in the patient's condition. However, these methods may present therapeutic, diagnostic, economic, or simply logistical drawbacks since confirmation of drug release from the implantable drug delivery device is not immediate and may be based on indirect or secondary indicators of release such as biomarkers or physiologic changes in the subject. Accordingly there is a need in the art for methods of assessing, during a visit to a health care provider, whether a therapeutic agent is being or has been properly delivered by an implantable drug delivery device. In particular, the ability to non-invasively visualize the inside of the eye provides an opportunity to develop methods for observing the condition of an implantable drug delivery device and confirming drug release while the drug delivery device resides in the subject's eye.
Examples of drug delivery devices for ophthalmic applications are described in the following, which are all incorporated herein by reference: U.S. Pat. No. 6,976,982, U.S. Pat. No. 7,582,080, US 2008/0221557, U.S. Pat. No. 7,776,024, AU 200241834, CN 2432438, EU 1372602, JP 4354521, JP 2002-555792, JP 2009-277085.